Polar 115 EMC freezes after reaching reference point.

Hi there!

Polar 115 EMC, S/N: 5136370. Right after coming on, operator presses front button to have back gauge reach reference point, display shows data then operator releases button and display goes blank, keys are unresponsive afterwards. Machine is turned off and then back on with same results.

Voltages have been checked to be within specs. At certaing point during troubleshooting, machine started right and was even able to cut paper. Machine was turned off and on about three times only to stop operating a few minutes after turning it off and back on a fourth time. Suspecting that CPU card was bad, tried to pull out socketed ICs for cleaning. Unfortunately, all socketed ICs have Gnd and Vcc pins soldered into the sockets and not having anticipated that, EPROM in position 10 (has 1.8.80 and number 4 printed on a sticker covering the quartz window) was pulled out and Vcc lead broke off from IC.

Trying to remedy that, then GND pin was unsoldered and IC pulled out in order to copy its contents into a new 2716 EPROM. A new Vcc lead was soldered in and EPROM placed in EPROM programmer ZIF socket to copy. Contents didn't look right (low order 4 bits read all zeroes and high order 4 bits read either 8s or 0s in all locations), so I re-read EPROM and every time I did, reading it produced a different checksum. Doing a Verify produced between 56 and 60 errors time and time again.

This IC was manufactued on the 52nd week of 1980. I wonder if these EPROMS start to have retention problems after all these years, which would be normal, I pressume. I wonder if the code in charge of scanning keyboard resides in this IC and that may be the reason why it stops operating once microprocessor tries to execute an invalid instruction code, or maybe the problem is elsewhere and EPROM started to act up after breaking the lead off. Either way, a good working EPROM is required.

Does anybody have a copy of CPU firmware to share? Maybe Superchock in his infinite bag of tricks has it?

Thanks in advance for your help

rlarios

 

Well, I was finally able to read these EPROMs. It turns out that Intel D2716s need to have +5V on PGM pin, and my EPROM programmer didn't do that. How did I find out? Well, I put together an EPROM reader with Arduino, and I didn't think PGM pin was important, so I left it floating. After reading the chip, I got all zeroes. Then, upon checking on Intel's D2716 datasheet, I realized that it had to have +5V on PGM. I wired this pin to +5V and voilá! It worked! I could read the contents of these Intel EPROMs. Then I checked this pin on my EPROM programmer and it turned out it put out +2V while reading it which produced same results (all zeroes and 8s) which doesn't seem to affect NEC, ST, or other brand chips. I used a jumper wire between +5V and PGM on my programmer, I read the chip again and now it worked.

I burnt a new set of EPROMs using NEC chips and installed them in the CPU board and off I went to test the cutter. It didn't work. It didn't do a thing after backgauge scanning for its reference point. I ended up removing the "new" EPROMs and re-installed the old ones, and now it did find the reference point and numbers on dispaly were changing but upon releasing the front handle while back gauge was moving forward, display went blank and I got back to square 1.

I wonder what software does right after releasing the front handle once reference point has been reached. Is it waiting for something else? Is N-KB board malfunctioning? Do not miss next episode.